George W. Bush Library Dedication

Barbara Bush (L) and Laura Bush (R) wait as US President Barack Obama (2L), former US President George W. Bush (C) and former US President George H. W. Bush arrive for a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

(L-R) First lady Michelle Obama, U.S. President Barack Obama, former first lady Barbara Bush and former President George H.W. Bush attend the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Kevork Djansezian/Getty Images)

George W. Bush Library Dedication

Former US President George H. W. Bush shakes hands with his son, former US President George W. Bush's, during a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University on April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

US President Barack Obama laughs as he chats with former First Lady Barbara Bush during the opening ceremony of the George W. Bush Presidential Center April 25, 2013 on the campus of Southern Methodist University (SMU)in Dallas, Texas. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

US President Barack Obama (R) and former President George W. Bush shakes hands during the opening ceremony of the George W. Bush Presidential Center April 25, 2013 on the campus of Southern Methodist University (SMU)in Dallas, Texas. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

(L-R) Former US Secretary of State Condoleezza Rice, Former US Vice President Dick Cheney, Jenna Bush Hager, her husband Henry Hager, Barbara Bush, John Ellis Bush, Jr. and his father former Florida Governor Jeb Bush sing the national anthem during the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. ( JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

Former US President George W. Bush hugs his wife Laura Bush as President Barack Obama and First Lady Michelle Obama look on during the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

(L-R) US First Lady Michelle Obama, President Barack Obama, former First Lady Barbara Bush, former President George H.W. Bush, former President George W. Bush and Laura Bush pray during the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

Former US President George H.W. Bush (C) and George W. Bush (2nd-R) sit with former First Ladies Barbara Bush (L) and Laura Bush (R) during the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

(L-R) US First Lady Michelle Obama, US President Barack Obama former First Lady Barbara Bush, former President George H.W. Bush, former President George W. Bush and former US First Lady Laura Bush laugh during the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

US President Barack Obama (L) and former presidents (L-R) George W. Bush, Bill Clinton, George H.W. Bush and Jimmy Carter arrive on stage for the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

Barbara Bush (L) and Laura Bush (R) wait while former US President George H. W. Bush and former US President George W. Bush shake hands during a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

(L-R) U.S. President Barack Obama, former President George W. Bush and former President Bill Clinton attend the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Alex Wong/Getty Images)

George W. Bush Library Dedication

Former US First Lady Laura Bush attends the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

Former US President George H.W. Bush attends the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

Former US First Lady Barbara Bush smiles during the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

US President Barack Obama (L) claps while Barbara Bush (2L) and former US President George W. Bush (R) smile as former US President George H. W. Bush waves to supporters during a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

Former US President George W. Bush smiles during the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

Former US President George W. Bush (L) and Laura Bush listen as former US President Clinton speaks during a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

US First Lady Michelle Obama (L) and former First Ladies (L-R) Laura Bush, Hillary Clinton, Barbara Bush and Roslyn Carter arrive on stage to attend the George W. Bush Presidential Center dedication ceremony in Dallas, Texas, on April 25, 2013. (JEWEL SAMAD/AFP/Getty Images)

George W. Bush Library Dedication

U.S. President Barack Obama (L) and former President George W. Bush attend the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Alex Wong/Getty Images)

George W. Bush Library Dedication

Former U.S. Vice President Dick Cheney (3rd L) is acknowledged as (L-R) Former British Prime Minister Tony Blair, former U.S. Secretary of State Condoleezza Rice, George W. Bush's daughter Jenna Bush Hager, her husband Henry Hager, and sister Barbara Bush applaud during the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Alex Wong/Getty Images)

George W. Bush Library Dedication

US President Barack Obama speaks during a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

Former First Lady Barbara Bush (R) speaks with US First Lady Michelle Obama (L) and US President Barack Obama during a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

Former US President George W. Bush finishes his speech during a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

(L-R) U.S. first lady Michelle Obama; President Barack Obama, former first lady Barbara Bush, former President George H.W. Bush, former President George W. Bush and his wife former first lady Laura Bush attend the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Alex Wong/Getty Images)

George W. Bush Library Dedication

(L-R) US President Barack Obama, former US President George W. Bush, former US President Bill Clinton, former US President George H. W. Bush and former US President Jimmy Carter arrive for a dedication ceremony as former US First Lady Laura Bush looks on, at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

From left US President Barack Obama, First Lady Michelle Obama, former First Lady Laura Bush and former US President George W. Bush depart after a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

Former President George W. Bush (L) waves goodbye after attending the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Kevork Djansezian/Getty Images)

George W. Bush Library Dedication

Former U.S. Secretary of State Colin Powell (L) speaks with former Prime Minister of Israel Ehud Olmert after they attended the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Kevork Djansezian/Getty Images)

George W. Bush Library Dedication

Former U.S. Secretary of State Condoleezza Rice (C) and Colin Powell (L) speak with former Prime Minister of Israel Ehud Olmert after they attended the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Kevork Djansezian/Getty Images)

George W. Bush Library Dedication

New Jersey Governor Chris Christie arrives for a dedication ceremony at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

Former President of South Korea Lee Myung-bak (L) speaks with former Italian Prime Minister Silvio Berlusconi at the George W. Bush Library and Museum on the grounds of Southern Methodist University April 25, 2013 in Dallas, Texas. (BRENDAN SMIALOWSKI/AFP/Getty Images)

George W. Bush Library Dedication

Former President George W. Bush (C) shakes hands with former President Bill Clinton (R) after his speech as former first lady Laura Bush looks on during the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Kevork Djansezian/Getty Images)

George W. Bush Library Dedication

President Barack Obama (L) shakes hands with former President George W. Bush before speaking at the opening ceremony of the George W. Bush Presidential Center April 25, 2013 in Dallas, Texas. (Photo by Kevork Djansezian/Getty Images)